Commit Message

From: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
I guess these fields were one day 16-bit in the struct but
nowadays they're just using 8 bits anyway.
This is just a precaution, didn't result any change in my
case but who knows what all those varying gcc versions &
options do. I've been told that 16-bit is not so nice with
some cpus.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
---
net/ipv4/tcp_output.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

Comments

"Ilpo Järvinen" <ilpo.jarvinen@helsinki.fi> writes:
> From: Ilpo JÃ¤rvinen <ilpo.jarvinen@helsinki.fi>>> I guess these fields were one day 16-bit in the struct but> nowadays they're just using 8 bits anyway.>> This is just a precaution, didn't result any change in my> case but who knows what all those varying gcc versions &> options do. I've been told that 16-bit is not so nice with> some cpus.
Typically when 16bit is not nice, 8bit isn't nice either.
For general flags the most save in terms of uniform performance
is "int"
-Andi

From: Andi Kleen <andi@firstfloor.org>
Date: Sun, 01 Mar 2009 03:39:02 +0100
> "Ilpo Järvinen" <ilpo.jarvinen@helsinki.fi> writes:> > > From: Ilpo JÃ¤rvinen <ilpo.jarvinen@helsinki.fi>> >> > I guess these fields were one day 16-bit in the struct but> > nowadays they're just using 8 bits anyway.> >> > This is just a precaution, didn't result any change in my> > case but who knows what all those varying gcc versions &> > options do. I've been told that 16-bit is not so nice with> > some cpus.> > Typically when 16bit is not nice, 8bit isn't nice either.> For general flags the most save in terms of uniform performance> is "int"
It's really only the truly ancient alpha cpus where this is
a measurable issue. Those chips only have 32-bit loads
and stores, so ever sub-32-bit access involves a 32-bit
load/store and a bunch of byte extraction instructions.
I don't think it's a relevant concern today. Especially
on x86 if that's why you are alluding to Andi.
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On Sat, Feb 28, 2009 at 07:08:45PM -0800, David Miller wrote:
> From: Andi Kleen <andi@firstfloor.org>> Date: Sun, 01 Mar 2009 03:39:02 +0100> > > "Ilpo Järvinen" <ilpo.jarvinen@helsinki.fi> writes:> > > > > From: Ilpo JÃ¤rvinen <ilpo.jarvinen@helsinki.fi>> > >> > > I guess these fields were one day 16-bit in the struct but> > > nowadays they're just using 8 bits anyway.> > >> > > This is just a precaution, didn't result any change in my> > > case but who knows what all those varying gcc versions &> > > options do. I've been told that 16-bit is not so nice with> > > some cpus.> > > > Typically when 16bit is not nice, 8bit isn't nice either.> > For general flags the most save in terms of uniform performance> > is "int"> > It's really only the truly ancient alpha cpus where this is> a measurable issue. Those chips only have 32-bit loads> and stores, so ever sub-32-bit access involves a 32-bit> load/store and a bunch of byte extraction instructions.
Yes old Alpha is the only one I know, although I don't claim to know every
weirdness of every embedded CPU out there.
My point was merely that 16bit is not in any way better than 8 bit.
> > I don't think it's a relevant concern today. Especially> on x86 if that's why you are alluding to Andi.
x86 normally[1] doesn't care, but it also doesn't save anything normally
for a on stack (or in register) variable because there's typically
padding anyways.
[1] there are some issues on older Intel CPUs with partial register
stall in a few cases.
-Andi

From: "Ilpo Järvinen" <ilpo.jarvinen@helsinki.fi>
Date: Sat, 28 Feb 2009 16:44:42 +0200
> From: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>> > I guess these fields were one day 16-bit in the struct but> nowadays they're just using 8 bits anyway.> > This is just a precaution, didn't result any change in my> case but who knows what all those varying gcc versions &> options do. I've been told that 16-bit is not so nice with> some cpus.> > Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Applied.
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